yep . pull and plug the vacuum first of course , then set the timeing to ~16 .Drive it around and see how it drives . I had a heck of a time figuring out how to set up the carb ( would have been nice if this forum existed way back then) .and That's what worked for me anyways .I knew when i had the carb dialed in i could stop at a light and turn a corner it always ran well and the same.hope it works for you

Setting the timing at 16deg is just masking the root cause of the problem
I've thought about this more and there are compounding issues

Quote:

Originally Posted by DonAltman3

.....Checked timing once again. Yup. 11-12 it kinda bounces between the two marks. Seems to have run better when I moved to 9-10. I used vacuum gauge its at 15 regardless of timing with ported blocked off and using manifold to check. Could I be doing this wrong I used a hand brake bleeder vacuum with gauge to check just took the part u usually go to a bleeder and put the manifold there it pulled 15-16 I released pressure each time a moved the distributor. I got pinging at high throttle at 11-12 timing. None at 9-10 with about the same performance. No noticeable vaccum leaks.

What I have highlighted is where this starts
The timing mark should not jump and 15' of vacuum in the manifold is on the low side
You either have a sloppy timing chain, dist drive gear or a vacuum leak
Its a direct indicator
Have you re-torqued your manifold bolts lately? The original ones have a tendancy to come loose over time

Your chain slack has been mentioned before

Quote:

Originally Posted by DonAltman3

Should I have also capped off manifold pressure from the pcv valve too or just ported to distributor vaccum advance? Ps I didn't understand your vaccum advance adjustment turns remark. Do I have to physically adjust the advance valve on the distributor? I"ve never done anything to it but hook a vacuum line to it. However it was originally installed by a mechanic shop perhaps they adjusted it.

Please explain this statement
The PCV doesn't need to be touched for any of these tuning processes as long as your valve is working correctly
Take that bleeder pump and put a vacuum on the advance can to make sure it doesn't leak down
And make sure your vacuum gauge doesn't leak down on its own

I don't see a major problem here, just down to correct tuning
Yes, fuel may be an issue but with a fresh fuel pump you may have more pressure than you need and it's stumbling from not enough air
A regulator may be in order
Even with the return on the filter, I had to put one on my Holley to get rid of the richness I was experiencing
The MC and Holley carbs don't want as much pressure as the fcty Carter
And make sure the return port on the filter is at the top

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setting the timing at 16 isn't masking anything and it's not meant to be a fix. It is simply taking the timing advance out of the picture to allow the OP to set his carb up properly . Once he has the carb set up 100% and it is running properly day/night ,hot/cold , he can set the timing properly and connect up his vac adv . Now he doesn't have to be concerned with the carb and driveability issues will be strictly timing related .

I hope this helps some. This is so frustrating. The problem seems so random. After trying a "fix" I usually leave my neighborhood onto a county road.. I usually get a mile or two down the road and it starts to sputter.. sometimes it works itself through it and recovers for a few minutes.. sometimes it stalls out instantly. Most times it cranks right back up I can rev the engine a couple of times and be off again.. then it boggs to a stall and I have to sit. It spins and spins a few minutes later it fires up like everything is fine. I've had it bucking spitting reving up then bogging and just feathered the throttle and eventually it settled down only to fall right back on its face a few mintues later. Stalling in traffic is SCARY but I'm so used to it I'm just more annoyed. My wife is tierd of "rescuing me" with a pull strap. This WAS and IS my only source of transportation and is a daily driver for me. Thanks for all of you helping me to brain storm, maybe I can get this thing going.

Quote:

Originally Posted by zeus87gn

The timing mark should not jump It is totally jumping between 2 degrees at any timing setting I put it on. Using my light it goes up down/up down alternating for miliseconds. Also the most I could get was 15-16 hg of vacuum.. it didn't change any when I moved timing around. I was just going to try to time the engine using vacuum since I was getting that weird problem with my timing mark jumping.

and 15' of vacuum in the manifold is on the low side
You either have a sloppy timing chain, dist drive gear or a vacuum leaknot sure on timing chain as I have been un-able after work to take down the front side of this motor to check it.. I've never looked at one on a jeep so I'm not even sure how...the distributor is fairly new but perhaps the gear could be worn?!?

Have you re-torqued your manifold bolts lately? The original ones have a tendancy to come loose over time

No I haven't.. running over all my issues I was thinking that too this morning.. perhaps I'm sucking some air at the intake manifold gasket... (I can't hear it but its possible)

Please explain this statement
The PCV doesn't need to be touched for any of these tuning processes as long as your valve is working correctly

After I tried to set timing and used ported advance it was mentioned to me to try manifold advance.. I wasn't sure if I needed to block off pcv valve or the inlet it goes to when resetting my timing like I did with the blocked ported vacuum to the distributor.. My pcv ties directly into the rear bottom inlet of the mc2100 what I think is manifold vacuum.

Take that bleeder pump and put a vacuum on the advance can to make sure it doesn't leak down

I defiantly can do this.. (ps it is less than a year old and I noticed last night it was a motorcraft reman distributor I got from NAPA)

And make sure your vacuum gauge doesn't leak down on its own It doesn't

The MC and Holley carbs don't want as much pressure as the factory Carter
And make sure the return port on the filter is at the top

The return port is on top and my last mc2100 carb has a fitting that screwed into the carb inlet it was what looked like a brass reducer with a hose nipple on it.. was this a "pressure reducer?" I removed it when I was thinking I was fuel starved and just put a brass hose barb into the carb that came with the new carb.

You ARE checking and setting your timing with the vacuum advance tube pulled and the plugged correct ? ( sorry if that is insulting at all ,but that sounds exactly like what happens if the vacuum is still connected)

setting the timing at 16 isn't masking anything and it's not meant to be a fix. It is simply taking the timing advance out of the picture to allow the OP to set his carb up properly

But you can't set up a carb until the engine is timed correctly
Disconnecting the hose from the vacuum advance takes it out of the picture

Quote:

Originally Posted by yzjwk

Once he has the carb set up 100% and it is running properly day/night ,hot/cold , he can set the timing properly and connect up his vac adv

The carb has to be close enough for the engine to run while you set the timing
Once the base timing is set, then you adjust the carb
Then you dial in the vacuum advance diaphgram
8-10deg is plenty of base timing

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Ah, more information, good
Did you replace it?
How long ago?
Do you know if the gear on the end was swapped with the original?

Quote:

Originally Posted by DonAltman3

After I tried to set timing and used ported advance it was mentioned to me to try manifold advance.. I wasn't sure if I needed to block off pcv valve or the inlet it goes to when resetting my timing like I did with the blocked ported vacuum to the distributor.. My pcv ties directly into the rear bottom inlet of the mc2100 what I think is manifold vacuum.

Quote:

Originally Posted by yzjwk

You ARE checking and setting your timing with the vacuum advance tube pulled and the plugged correct ?

Yes, lets please all be on the same page

Quote:

Originally Posted by DonAltman3

...my last mc2100 carb has a fitting that screwed into the carb inlet it was what looked like a brass reducer with a hose nipple on it.. was this a "pressure reducer?" I removed it when I was thinking I was fuel starved and just put a brass hose barb into the carb that came with the new carb.

Nope, that was not a fuel pressure regulator, just a hose fitting of some sort

To check the slack in your chain is all too easy
Get a socket wrench to turn the motor at the crank
Remove the dist cap and lay it out of the way
Rotate the engine a bit (correct rotation) so you see the rotor turn with the crank
Now rotate the crank backwards slowly and watch the rotor
If there is any chain slop, the rotor will lag behind the crank

Some folks say that some slack is acceptable - I don't agree

__________________
Handicapped license plates are not for mentally handicapped people -

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But you can't set up a carb until the engine is timed correctly
Disconnecting the hose from the vacuum advance takes it out of the picture

I disagree , the engine IS timed properly , or it wouldn't run at all . The ADVANCE timing has nothing to do with how well an engine runs .People run and even RACE their vehicles with no vacuum advance at all .

The carb has to be close enough for the engine to run while you set the timing
Once the base timing is set, then you adjust the carb
Then you dial in the vacuum advance diaphgram
8-10deg is plenty of base timing

EXACTLY The base timing IS set up . All I'm saying is leave the advance off while you get the carb set up . Setting the base timing higher is just so the op can drive around for a few days better while he makes adjustments to the carb .Having the advance connected is just compounding problems if the op has problem in both areas .

You ARE checking and setting your timing with the vacuum advance tube pulled and the plugged correct ? ( sorry if that is insulting at all ,but that sounds exactly like what happens if the vacuum is still connected)

Yes I set timing with it plugged at both the distributor side and the port on the carb that is "ported" advance.

Ah, more information, good
Did you replace it?
How long ago?
Do you know if the gear on the end was swapped with the original?

I am pretty sure this was a complete unit.. including the gear ordered specifically for my jeep from napa part number is 48-4691 it was purchased 12/22/2011 It probably only has 10,000 miles on it since then as I drive less than 12 miles a day to work both ways and it isn't driven any on the weekends.

At that time a complete tune up was done, replaced coil w/an msd blaster canister coil, rebuilt my carb, replaced fuel pump and exhaust manifold gaskets (had a crack in it) ...I had it done by an 80 year old mechanic that everyone recommended as being "the guy" to work on carbureted things.. the jeep left there running better but still had a problem... I decided to do a nutter bypass..

I learned to nurse the jeep or not use it on the highway for the last year or so until it recently got so bad I convinced myself his carb rebuild was trash and I should just buy a new one..... that's where this has all come from.

I purchased a new one.. same symptoms only now it idles better. I upgraded the stock ignition the ford style "team rush" upgrade.. I went to 8mm wires from my old 7mm wires,new ford cap and button new delco plugs. Honestly couldn't tell any difference. New fuel pump, new fuel filters. My old plugs looked a little lean. I thought the problem might be the sending unit.. I ran a gas can in my floorboard with a line directly to the pump.. still had the problem So I eliminated trash in the fuel system or tank.
I removed and blocked off EGR jeep doesn't have emission control on it.. no catalytic converter.

And when it runs for the first little bit (set at 8 or 9 initial timing) it runs pretty good until it starts the bogging and stalling... tthis usually happens after driving a couple of miles doesn't seem to matter if I take it easy or if I get on it pretty good.

Yes I set timing with it plugged at both the distributor side and the port on the carb that is "ported" advance.

Ok, good - but you only need plug it at the dist end
Move the other end from ported at the carb to direct manifold - there should be a port behind the carb pointing up
Cap off the carb port

Quote:

Originally Posted by DonAltman3

I am pretty sure this was a complete unit.. including the gear ordered specifically for my jeep from napa part number is 48-4691 it was purchased 12/22/2011 It probably only has 10,000 miles on it since then as I drive less than 12 miles a day to work both ways and it isn't driven any on the weekends.

Excellent - theres a good chance you got the right dist you need for this

Quote:

Originally Posted by DonAltman3

At that time a complete tune up was done, replaced coil w/an msd blaster canister coil, rebuilt my carb, replaced fuel pump and exhaust manifold gaskets (had a crack in it) ...I had it done by an 80 year old mechanic that everyone recommended as being "the guy" to work on carbureted things.. the jeep left there running better but still had a problem... I decided to do a nutter bypass..

Yes, definetely re-torque your manifold bolts...all of them - 27ftlbs

Quote:

Originally Posted by DonAltman3

I upgraded the stock ignition the ford style "team rush" upgrade.. I went to 8mm wires from my old 7mm wires,new ford cap and button new delco plugs. Honestly couldn't tell any difference. New fuel pump, new fuel filters. My old plugs looked a little lean.

Which plugs are they specifically?

Quote:

Originally Posted by DonAltman3

And when it runs for the first little bit (set at 8 or 9 initial timing) it runs pretty good until it starts the bogging and stalling... tthis usually happens after driving a couple of miles doesn't seem to matter if I take it easy or if I get on it pretty good.

Here is where the motor is getting warmed up and not getting proper combustion and the right time

Try this....
Warm up the engine and set the timing at 8 or 9deg, make your carb adjustments with the vac adv disconnected (hose plugged) and the idle speed about 100 to 150 rpms lower than you would really like it
Adjust your misture screws in until it starts to stumble, then back them out until it smoothes out - idle adj may be needed
Connect the vac adv to manifold vacuum and the idle speed should go up that 100-150 rpms
If it goes up to far or not enough, then you need to adjust the vac adv diaphragm with the 1/8" allen wrench

Needed timing is based on engine load - in the case of our old carb engines, this signal comes from direct manifold vacuum

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I disagree , the engine IS timed properly , or it wouldn't run at all . The ADVANCE timing has nothing to do with how well an engine runs .People run and even RACE their vehicles with no vacuum advance at all.

An engine will run with the timing set incorrectly
This is the exact problem Don has
The vacuum advance is the reason these engines runs so well

Quote:

Originally Posted by yzjwk

All I'm saying is leave the advance off while you get the carb set up.

This I will agree with

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I am going to go out on a limb here for a couple of reasons... I used to own an 88 YJ with the 4.2. However, it had a Weber 32/36 carb on it but I still had to chase vacuum issues to get the timing right...

Two things that have not been mentioned yet-

Have you checked the EGR valve?

and...

There is an EVAP canister under the brake master cylinder on the fender. Vacuum is connected to this canister. Under that cap on the top is a rubber diaphragm. On mine it was torn thus compromising the vacuum. Stick a hose down there while the engine is running and listen at the other end. Sucking noise?

It was after I checked the intake/exhaust manifolds, the carb plate gasket, valve cover, vacuum lines, installed a fuel pressure regulator, unbound the drive belt, put in a new PCV valve, new spark plugs, new wires, new battery, new battery cables, and finally the EGR valve, that the EVAP can vacuum leak was exposed.

Somewhere in a box around here I still have all the factory service manuals for the 88 YJ. Let me know if I can look up something for you...

An engine will run with the timing set incorrectly
This is the exact problem Don has
The vacuum advance is the reason these engines runs so well

This I will agree with

NOW you agree with me .
before it was and i quote " But you can't set up a carb until the engine is timed correctly
Disconnecting the hose from the vacuum advance takes it out of the picture"

Don I REALLY hope you can get this straitened out , but for now i will bow out and let Zeus try and help .there's more then 1 way to get to the bottom of this but too many roosters in the hen house for me .I know you guys can get this , but please if all else fails, feel free to PM me and i will help as much as possible .
Good luck guys

Jeep had some intake manifold bolts that felt kind of loose and the one closest to cab at rear bottom of engine looks like it came all the way out and got lost.. After tightening them down I tried to start jeep at timing 8 degrees. Would not start without really revving up engine. I could give throttle to keep it running. Tried to up idle speed on accelerator linkage adjustment. Didn't seem to help much. I only turned it a full turn or so before I stopped. I drove it though and seemed strong and a little more peppy. Eventually it stumbled but could of been me letting to far off the throttle or not shifting to neutral fast enough to slow down and keep rooms high enough. Vaccum was checked it went up to about 21. And I could hear the carb sucking air into it. I didn't hear this before. I guess all the air was being sucked into the manifold. I'm going to go over the manifold again under better cicumstances or pay a shop to replace gasket. Seemed like a total pita to get to some of those bolts. Once I have them not leaking 100%. Can someone explain to me like I'm five how to properly adjust the carb

Gosh I hope this is going to fix it. Maybe the leak was so gradual I just assumed it was my jeep carb getting more and more "tired"

Thanks again. I'm so happy to have made any progress tonight I'm calling it quits for now while I'm on a high note.